This project seeks to develop new statistical methodologies for problems in human development and to apply existing methodologies to those problems in novel ways. Work continues in two areas: (1) statistical modeling of the distribution of birthweights in human populations, and (2) statistical modeling of developmental trajectories of reproductive hormones in children through puberty. Development of a satisfactory statistical model for the distribution of birthweights in a population iwll facilitate a refined understanding of the relationship of birthweight to infant mortality. We have developed a model and a method for fitting the model to data that allow us to measure selected features of birthweight distributions. We are now applying our techniques to U.S. birthweight and perinatal mortality data to assess how well mortality rates arfe predicted by features of birthweight distributions that our technique measures. Serum levels of gonadotropins and gonadal hormones change as children develop through puberty. We have develope parsimonious descriptions of hormonal development through puberty by fitting certain nonlinear regression models to hte logarithm of hormone level as a function of either testis volume or Tanner stage. We are currently comparing developmental trajectories of FSH, LH, and inhibin between boys and girls.